Now let's prepare the brine. Place ¼ cup of salt into the quart jars with the whey in it. If there is a layer of cream swimming on top, skim it off first. Put a lid on the jar and shake vigorously to dissolve the salt. It's ok if it won't all dissolve right away, just give it another shake whenever you happen to think about it over the next day.
Here is the important part: The brine and the cheese need to age at the same temperature for the same amount of time. This takes care of all the important things that make a perfect brine and allow for successful brining of the cheese later. The calcium content in the whey is just what is needed to keep the cheese from melting later when it is aging in it. The acidity also must be the same and when you age the brine and the cheese at the same temperature for the same amount of time, the acidity will match. Soo… after mixing your brine, set the jar next to the cheese cakes and keep it there until you're ready to put the cheese in it. (If you are doubling this recipe, make 2 quarts of the brine!)
Now the cakes need to be salted.
First look at them to see if they would fit into your canning jar opening. If they are too big, cut the cakes into quarters. Sprinkle with plenty of salt all over all the surfaces and place them on the plate or rack to drain. It's important to cut them before salting because all the surfaces need to dry and form a rind.
After 12 hours, flip each of them over onto a dry surface and salt them again lightly. The goal is to develop the beginnings of a firmed-up 'rind' all around the exposed edges. This is important to prevent the pieces from dissolving in the brine.
Let them dry for another 12-24 hours, flipping once or twice more and placing them on a dry surface each time. It might take another day, up to 3 days total.
Once your feta chunks are firmed up a bit, it's time to age them. Take the second mason jar and carefully place the chunks of cheese into it.
Now carefully pour the brine down the sides of the jar (don't pour directly on the cheese). Fill the jar all the way up to the top. The chunks need to be submerged. Any that float to the top will most likely get moldy and might become ruined. So place a glass fermentation weight on the chunks, or a boiled flat rock, a broken chopstick, or some other non-corrosive object to keep the cheese down in the brine.
Now you'll want to age the cheese for 2 weeks at 50 degrees if you have a cheese cave, then move them to a 40 degree or below refrigerator. Or just put it in the fridge right away. It will still taste great. Let the cheese chunks age there for 6-8 weeks. If you want to eat some sooner it's totally fine, they are ok to eat now, but will need some time to mature into real feta. And they get better as they age! Allow for some to ripen for 6 months and compare the difference.
Whenever you want to eat a chunk, use a clean utensil and lift a piece out of the brine, make sure there are no floaters, and seal the jar back up. Don't put the piece you took out back later, just keep it in a separate container in the fridge and eat it within a week.